I would not bother checking the OVP relay, I would just replace it with the proper replacement part from either M/B or the aftermarket. Your symptoms are those of a failed OVP relay and even if it is not bad [unlikely] it needs to be replaced due to age. The OVP relay can develope internal, intermittant open circuits as well as having the fuse[s] blow due to jump starting the car or crossing the battery cables during battery replacement. Just replace it with a good quality relay and see what happens.